TABLE 5.

Mutations in ampC promoter and attenuator regions and cephalosporinase specific activity of selected E. coli isolates

Strain	Mutations in promoter and attenuatora	Cephalo- sporinase sp actb
DH5α	Same as E. coli K-12 control	1.00
EC689	−73, −66, −28, +17	2.59 ± 0.26
EC3076	−76, +22, +26, +27, +32	2.04 ± 0.13
EC3194	−76, +22, +26, +27, +32	2.67 ± 0.12
EC3358	No mutations detected	2.40 ± 0.09
Control strains
CDC10	−73, −28, 1-bp insert between −35 and −10, +17	13.6 ± 2.2
CDC110	−73, −32, +58	14.6 ± 1.3
CDC3100	−76, 2-bp insert between −35 and −10, +22, +26, +27, +32	17.2 ± 3.7

^aKey mutations associated with enhanced AmpC production are indicated by bold type.

^bSpecific cephalosporinase activities are relative values based on the activity in the wild type strain DH5α.